The VPLS service or Virtual Private LAN Service in English terminology is a service allowing the interconnection between a plurality of IP (Internet Protocol) communication networks, such as for example private networks or enterprise networks. The VPLS service makes it possible to connect together a plurality of IP networks corresponding for example to sites of one and the same enterprise that are distant from one another so as to form a multipoint-to-multipoint architecture.
An example of data-transmission technology used when the VPLS service is applied is the MPLS (MultiProtocol Label Switching) technology. The MPLS technology proposes adding as a data packet header one or more labels containing information allowing the items of network equipment to determine the next hop that a packet must make to reach its destination.
The MPLS technology is described in greater detail in a document of the Internet Engineering Task Force (the internet standardization group, abbreviated in English as the IETF), referenced RFC 3031 (RFC standing for Request For Comments in English).
When the VPLS service is applied, items of equipment belonging to various LAN networks are connected together by means of MPLS paths called LSPs (Label Switched Path).
An LSP path is established from an item of head terminal equipment (or Ingress equipment) via intermediate items of equipment and to an item of destination terminal equipment (or Egress equipment).
However, the MPLS technology makes it possible to process only packets that conform to the IP protocol.
In order to alleviate this drawback, the PWE3 (PseudoWire Emulation Edge to Edge) standardization group of the IETF defines a virtual circuit concept making it possible to emulate a two-way link between two items of equipment of two distinct LAN networks based on the IP/MPLS technology. Such pseudo-wires, defined in document RFC 3985, allow the transmission of data packets that do not conform to the IP protocol, such as for example data frames conforming to the Ethernet protocol as defined in the IETF document referenced RFC 4448.
Therefore, the VPLS service consists of the establishment of pseudo-wires conforming to the Ethernet protocol between items of communication equipment belonging to various networks. Such pseudo-wires are established on the data-link layer as defined in the OSI (Open Systems Interconnection) model defined by the ISO (International Standards Organization). The pseudo-wires thus established are for example pseudo-wires conforming to the Ethernet protocol. Such Ethernet pseudo-wires are supported by an underlying path such as links, for example tunnels conforming to the LSP (Label Switched Path) protocol defined in IETF document RFC 3031.
When the VPLS service is applied, each item of terminal equipment belonging to an IP network is connected to a plurality of other items of terminal equipment belonging to other IP networks by means of Ethernet pseudo-wires thus creating a connection between the various items of terminal equipment. However, such an architecture is fixed during the establishment of the various Ethernet pseudo-wires and does not change during the use of the VPLS service.
Therefore, when new pseudo-wires are required in order to connect other items of communication equipment together, the architecture underlying the use of the VPLS service is not adapted.